People who don't know anything about the process of a book to film adaptation. Clueless and idiotic "fans" who slate the Harry Potter films because they are "not like the books." These people fail to recognise that books and films are entirely separate mediums and entities.

They often resort to hating the director, not taking into account that there are other people involved in the filmmaking process, including the writers and WB Studios who place pressure on the team to adapt source material from a 700 page novel into a 2.5 hour film with budget constraints.

Potter purists lack any knowledge and common sense; they moan and whine about the slightest change, cut and/or addition in the films and are ignorant to the fact that such changes are necessary for the benefit of cinematic style and substance.

They also do not rate a film on its cinematic structure (EG editing, cinematography, pacing, score etc...) but on how much it was like the book.

Basically, they are generally a group of ungrateful haters, which Jo Rowling would be extremely ashamed to call "fans".